Selective expression of the insulin I gene in rat insulinoma-derived cell lines.

Four rat insulinoma-derived cell lines were found to express only the rat insulin I gene, although an apparently normal insulin II gene was present in each cell line. This finding was reflected by the absence of insulin II and the presence of insulin I gene transcripts in the products of run-on transcription assays, the absence of insulin II and the presence of insulin I unprocessed (pre-) mRNA, and the absence of mature insulin II and the presence of insulin I mRNA. Analysis of insulin II genes in cell lines by gene amplification indicated that the lack of insulin II gene transcription is not explained by the absence of or gross alterations in the insulin II genes per se. These studies indicate that the two nonallelic insulin genes do not function equivalently in pancreas-derived cells.